The present invention is directed to a float actuated shutoff valve employed to prevent overfilling of a liquid storage tank, such as an underground fuel storage tank, for example.
The typical underground fuel storage tank utilized in service stations throughout the United States has a capacity of several thousand gallons and is normally buried beneath the service station apron at a depth below the frost line. A fill pipe extends upwardly from the top of the tank to a supply hose coupling accessible within a relatively shallow manhole. To fill the tank, a supply hose from the tank truck is coupled to the fill pipe, and fuel is fed by gravity from the tank truck through the supply hose and fill pipe into the tank. The head space of the tank is normally provided with an atmospheric vent. In almost all cases, there is no gauge for indicating the state of fullness of the tank. In theory, the fuel delivery man is supposed to measure the amount of fuel in the tank prior to filling by inserting a dip stick through the fill pipe, and is prohibited from connecting the storage tank to a fuel compartment of the tank truck which has more fuel than can be placed in the storage tank without overfilling the storage tank. Unfortunately, this procedure is not always followed, and overfilling of the storage tank and the resultant spillage of fuel is a common occurrence.
As a result of environmental concerns, float actuated valves have been employed in increasing numbers to automatically close off or block the fill pipe when the level of fuel within the storage tank rises to a level indicating the tank is nearly full. The float actuated valves of the prior art typically employ a pivoted flapper valve in which the valve flapper or head is withdrawn into a recess at one side of the fuel inlet passage to the tank during filling and coupled to a float disposed within the tank to be pivoted outwardly into the flow path of the incoming fuel when the level within the storage tank rises to the selected level. The flapper is then driven to its seat with considerable force by the downwardly flowing fuel, resulting in a substantial water hammer effect when the rate of flow of fuel through the supply hose and fill pipe coupling is reduced from a typical rate of 400 gallons per minute to zero almost instantaneously.
In parent application Ser. No. 07/534,442 referred to above, this water hammer effect is minimized by employing a two-stage valve in which a first valve flapper is float actuated when the tank is approximately 90% full to close and partially, but not completely, block the incoming flow passage. With the passage partially blocked by closure of the first flapper, the rate of flow of fuel into the tank is substantially reduced, and the less severe water hammer generated by the partial closure can be observed by the delivery man who can, if he is so motivated, shut off the flow of fuel at the tank truck at a time when the storage tank has ample capacity to receive the 25 or 30 gallons remaining in the tank truck hose downstream of the tank truck shutoff valve. If, through inattention, the driver does not shut off the delivery hose upon closure of the first flapper, the subsequent rise in level of fuel in the tank will, when the tank is approximately 95% full, raise a second float which will close a second flapper which, with the closed first flapper, will completely block flow through the fill pipe. No more fuel will flow into the storage tank, and the driver can close the tank truck shutoff valve at leisure. Fuel trapped in the supply hose between the tank truck shutoff valve and the coupling can be drained into an overfill storage container such as that disclosed in U.S. Pat. No. 4,793,387.
In the two-stage shutoff valve shown in the aforementioned parent application, the flapper valves are mounted within a valve housing at the upper end of a drop tube projecting downwardly through the storage tank fill pipe into the tank. The supply hose coupling to which the tank truck supply hose is coupled during a filling operation is mounted at the top of the drop tube. In certain areas of the country, recently enacted regulations require that vapor expelled from the underground storage tank during a filling operation be returned to the tank truck during the filling operation rather than being vented to atmosphere. The most convenient way of accomplishing this vapor recovery is to employ an arrangement in which fuel is conducted into the storage tank via the drop tube which is loosely received within the storage tank fill pipe, and vapor passing upwardly through the space between the outside of the fuel carrying drop tube and the inside of the fill pipe is passed through the supply coupling to the tank truck hose coupling, from which it is conducted back to the tank truck. This is accomplished by mounting an adapter at the top of the storage tank fill pipe which has an enlarged central passage opening into the interior of the fill pipe and co-axially mounting, within the enlarged central passage of the adapter, the smaller diameter drop tube. The hose coupling on the tank truck hose fits around the outer side of the adapter, and the fuel flow passage through the hose coupling is sealed to the upper end of the drop tube when the hose coupling is mated to the fill pipe supply coupling. Passages through the hose pipe coupling conduct vapor from the fill pipe to a vapor transfer hose. With such an arrangement, it is impractical to mount the two-stage valve of parent application Ser. No. 07/534,442 at the top of the fill pipe, and the present invention is directed to a solution for that problem.
The valve flappers of parent application Ser. No. 07/534,442 are, as is typical with the prior art, mounted for pivotal movement about a horizontal axis, and when in their open position project vertically upwardly from the pivot axis. When in its open position, the flapper is located within a recess in the side of the flow passage so that the main stream of downwardly flowing incoming fuel passes in front of the flapper. Only a slight movement of the flapper from its open position will swing the top edge of the flapper into the main stream of the fuel, and once this occurs, the fuel stream overrides the flapper actuating mechanism and forcibly drives the flapper to its closed position. Because at least some of the incoming fuel will flow into the recess behind the flapper there is at least some possibility that this last flow could shift the flapper forwardly from its open position enough to cause a premature closure of the flapper.
The present invention provides a float actuated locking pin arrangement which will prevent such premature closure.